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received: 06 June 2016 accepted: 04 January 2017 Published: 07 February 2017
Assessing of the contributions of pod photosynthesis to carbon acquisition of seed in alfalfa (Medicago sativa L.) Wenxu Zhang1, Peisheng Mao2, Yuan Li3, Mingya Wang2, Fangshan Xia2 & Hui Wang2 The distribution of carbon from a branch setting pod in alfalfa was investigated during the seed development of seeds to determine the relative contribution of pod and leaf photoassimilates to the total C balance and to investigate the partitioning of these photoassimilates to other plant organs. A 13 Clabeling procedure was used to label C photoassimilates of pods and leaves in alfalfa, and the Δ13C values of a pod, leaves, a section of stem and roots were measured during seed development on day 10, 15, 20 and 25 after labeling of the pod. The results showed that the alfalfa pod had photosynthetic capacity early in the development of seeds, and that pod photosynthesis could provide carbon to alfalfa organs including seeds, pods, leaves, stems and roots, in addition to leaf photosynthesis. Photosynthesis in the pod affected the total C balance of the alfalfa branch with the redistribution of a portion of pod assimilates to other plant organs. The assimilated 13C of the pod was used for the growth requirements of plant seeds and pods. The requirements for assimilated C came primarily from the young pod in early seed development, with later requirements provided primarily from the leaf. Alfalfa (Medicago sativa L.) is the most widely cultivated forage legume in temperate areas and is a predominant component in mixtures for hay, silage and pasture. In China, more than 1.6 million hm2 are planted to alfalfa, with the agronomic value primarily in cultivation for forage production rather than seed yield. However, the ability of a cultivar to provide a high seed yield determines the competitive selling price, which is a key factor for the effective distribution of a cultivar to farmers1. The demand for alfalfa seed has gradually increased and is expected to continue, reaching 30,000–40,000 t in the next 5 years in China. However, at current levels, the domestic seed production would only meet approximately one-third of the future demand. Because of the characters of perennial growth and indefinite inflorescence, the seed yield of alfalfa is low, which limits the distribution of cultivars; consequently, the alfalfa seed yield is low and unstable (201–915 kg ha−1) in China2. Therefore, to improve the yield of alfalfa seeds, research on the development and maturity of seeds is urgently required. Most of the crop yield, 90–95%, is the result of photosynthesis. Although green leaves are generally the primary source of photosynthetic production, reproductive organs that are photosynthetically active can also determine yields3,4. Some non-leaf organs contain chlorophyll and have photosynthetic capacity, including the pod in rapeseed (Brassica napus L.), garden pea (Pisum sativum) and soybean (Glycine max L.)5–11. As primarily heterotrophic organs, seeds are dependent on nutrients supplied by the photosynthetic organs for the synthesis of reserves during development. In studies of pea, a significant portion of seed carbon is assimilatedby the pod7,12. Similar to the pea, does the pod in alfalfa have photosynthetic capacity, and does pod photosynthesis contribute to seed production in alfalfa? These questions remain unanswered because pod photosynthesis in alfalfa has not been investigated.
1
Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education of China, Key Laboratory of Gansu Polymer Materials, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou 730070, China. 2Institute of Grassland Science, China Agricultural University, Beijing 100193, China. 3Dryland Farming Institute, Hebei Academy of Agricultural and Forestry Sciences, Hengshui 053000, China. Correspondence and requests for materials should be addressed to W.Z. (email:
[email protected]) or P.M. (email: maops@ cau.edu.cn)
Scientific Reports | 7:42026 | DOI: 10.1038/srep42026
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Figure 1. Changes for Δ13C values (‰) in the alfalfa organs (P, SEED, L1, L2, L3, S and R) according to the development stage (from day10 to 20 after podding) after pod or leaves labeling. Each value represents the mean ± SE (n = 3). The different letters indicate significant differences (P
